Semiconductor light-emitting device

ABSTRACT

A semiconductor light-emitting device includes a first conductivity-type semiconductor including a first electrode on a first main surface, a second conductivity-type semiconductor, and an active layer between a second main surface of the first conductivity-type semiconductor and a first main surface of the second conductivity-type semiconductor. Protrusions are disposed in at least part of a region of a second main surface of the second conductivity-type semiconductor facing the first electrode. A second electrode is disposed in at least part of a region of the second main surface of the second conductivity-type semiconductor except the region having the protrusions. The protrusions containing a dielectric material protrude from the second main surface of the second conductivity-type semiconductor in a direction away from the active layer and are separated by intervals longer than the wavelength of light emitted from the active layer in the medium of the protrusions.

BACKGROUND

1. Field

The present disclosure relates to a semiconductor light-emitting device.

2. Description of the Related Art

FIG. 20 is a schematic cross-sectional view of a GaAs infraredlight-emitting device disclosed in Japanese Patent No. 3312049. The GaAsinfrared light-emitting device illustrated in FIG. 20 includes a p-typesemiconductor layer 111, an n-type semiconductor layer 112, ap-electrode 115 disposed on the p-type semiconductor layer 111, andseparated n-electrodes 116 disposed on the n-type semiconductor layer112. The p-type semiconductor layer 111 and the n-type semiconductorlayer 112 have a PN junction plane 113 therebetween. The n-typesemiconductor layer 112 has a V-shaped groove 117, which divides the PNjunction plane 113. The surface of the n-type semiconductor layer 112not covered with the n-electrodes 116 is substantially entirely coveredwith a reflective film 114. The reflective film 114 is a dielectricoptical multilayer film.

In the GaAs infrared light-emitting device illustrated in FIG. 20, theV-shaped groove 117, which divides the PN junction plane 113, faces thep-electrode 115 disposed on the light emitting surface. Thus, theV-shaped groove 117 reduces the area of the PN junction plane 113 facingthe p-electrode 115. It is therefore argued that the V-shaped groove 117can reduce the amount of light traveling from the PN junction plane 113to the p-electrode 115 and thereby reduce the amount of light blocked bythe p-electrode 115 and improve light emission efficiency.

FIG. 21 is a schematic cross-sectional view of a micro LED arraydisclosed in Japanese Patent No. 4830356. The micro LED arrayillustrated in FIG. 21 includes a transparent electrode 121 containingindium tin oxide (ITO), an n-electrode 122 embedded in part of thetransparent electrode 121, an n-type GaAs layer 123 disposed on thetransparent electrode 121 and the n-electrode 122, an n-type AlGaInPlayer 124 disposed on the n-type GaAs layer 123, a multiple quantum well(MQW) active layer 125 disposed on the n-type AlGaInP layer 124, the MQWactive layer 125 including an AlGaInP layer and a GaInP layeralternately stacked on top of one another, a p-type semiconductor layer126 including a p-type AlGaInP layer and a p-type GaInP layer, thep-type semiconductor layer 126 having a textured structure including apair of inclined reflective (111) and (11-1) planes, alow-refractive-index film 127 filling part of the textured structure ofthe p-type semiconductor layer 126, a p-type GaAs layer 128 disposed onthe p-type semiconductor layer 126, a p-electrode 129 covering thetextured structure of the p-type semiconductor layer 126 and the p-typeGaAs layer 128, a light reflecting metal layer 130 disposed on thep-type semiconductor layer 126 and covering the p-electrode 129, a leadelectrode 132 disposed on and electrically connected to the lightreflecting metal layer 130, a mold resin layer 131, and a concave mirror133 having a large radius of curvature.

Each of the p-type AlGaInP layer and the p-type GaInP layer of thep-type semiconductor layer 126 contains phosphorus. Thus, the inclinedreflective surfaces of the p-type semiconductor layer 126 are formed bywet etching using hydrochloric acid as an etchant utilizing differentetch rates of different crystal faces. The pair of inclined reflectivesurfaces of the p-type semiconductor layer 126 form a V-shaped groove,which does not reach the MQW active layer 125.

In the micro LED array illustrated in FIG. 21, it is argued that thepair of inclined reflective surfaces of the p-type semiconductor layer126 can confine the electric current between these inclined reflectivesurfaces and allows the electric current to flow into a limited regionof the MQW active layer 125 rather than a nonradiative recombinationregion, such as an end surface of the device, thus improving luminousefficiency.

In the GaAs infrared light-emitting device illustrated in FIG. 20 anddescribed in Japanese Patent No. 3312049, however, the V-shaped groove117, which divides the PN junction plane 113, reduces the area of the PNjunction plane 113 that is involved in light emission and therebyreduces light extraction efficiency. When the device structureillustrated in FIG. 20 is applied to a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1), in order to sufficientlyactivate the p-type semiconductor layer 111, the p-type semiconductorlayer 111 can contain p-type GaN or p-type AlGaN having a low Alcontent. However, such a p-type semiconductor layer 111 greatly absorbslight emitted from the PN junction plane 113 and reduces lightextraction efficiency.

When the device structure illustrated in FIG. 21 and described inJapanese Patent No. 4830356 is applied to a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1), in order to sufficientlyactivate the p-type semiconductor layer 126, the p-type semiconductorlayer 126 can contain p-type GaN or p-type AlGaN having a low Alcontent. However, p-type GaN and p-type AlGaN having a low Al contentare resistant to wet etching, making it difficult to form the inclinedreflective surfaces. When the transparent electrode 121, for example,containing ITO is applied to a semiconductor light-emitting devicecontaining Al_(x)Ga_(y)N (0<x≦1, 0≦y<1), the transparent electrode 121has a great optical absorption loss and reduces light extractionefficiency.

SUMMARY

A semiconductor light-emitting device according to an embodimentdisclosed herein is a semiconductor light-emitting device containingAl_(x)Ga_(y)N (0<x≦1, 0≦y<1). The semiconductor light-emitting deviceincludes a first conductivity type semiconductor, a second conductivitytype semiconductor, an active layer between the first conductivity typesemiconductor and the second conductivity type semiconductor, firstelectrodes disposed on a first main surface of the first conductivitytype semiconductor, a second electrode disposed on a second main surfaceof the second conductivity type semiconductor, and protrusions disposedon the second main surface of the second conductivity typesemiconductor. The first main surface of the first conductivity typesemiconductor faces the second main surface of the second conductivitytype semiconductor with the first conductivity type semiconductor, theactive layer, and the second conductivity type semiconductor interposedtherebetween. The protrusions are disposed in at least part of a regionof the second main surface of the second conductivity type semiconductorfacing each of the first electrodes. The second electrode is disposed inat least part of a region of the second main surface of the secondconductivity type semiconductor other than the region in which theprotrusions are disposed. The protrusions protrude from the second mainsurface of the second conductivity type semiconductor in a directionaway from the active layer. The protrusions contain a dielectricmaterial. The protrusions are separated by an interval longer than thewavelength of light emitted from the active layer in the medium of theprotrusions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a semiconductorlight-emitting device according to a first embodiment;

FIG. 2 is a schematic enlarged cross-sectional view of a portion withinthe broken line in FIG. 1;

FIG. 3A is a schematic plan view of the protrusions viewed in thedirection of the arrow in FIG. 2, and FIG. 3B is a schematic plan viewof one of the protrusions;

FIGS. 4A to 4C are schematic views illustrating the principle ofcontrolling the direction of light reflection with protrusions;

FIG. 5 is a schematic cross-sectional view illustrating a method formanufacturing the semiconductor light-emitting device according to thefirst embodiment;

FIG. 6 is a schematic cross-sectional view illustrating a method formanufacturing the semiconductor light-emitting device according to thefirst embodiment;

FIG. 7 is a schematic cross-sectional view illustrating a method formanufacturing the semiconductor light-emitting device according to thefirst embodiment;

FIG. 8 is a schematic cross-sectional view illustrating a method formanufacturing the semiconductor light-emitting device according to thefirst embodiment;

FIG. 9 is a schematic cross-sectional view illustrating a method formanufacturing the semiconductor light-emitting device according to thefirst embodiment;

FIG. 10 is a schematic cross-sectional view illustrating a method formanufacturing the semiconductor light-emitting device according to thefirst embodiment;

FIG. 11 is a schematic cross-sectional view illustrating a method formanufacturing the semiconductor light-emitting device according to thefirst embodiment;

FIG. 12 is a schematic cross-sectional view illustrating a method formanufacturing the semiconductor light-emitting device according to thefirst embodiment;

FIG. 13A is a schematic plan view illustrating the positionalrelationship between a first electrode and a second electrode in asemiconductor light-emitting device according to a second embodiment,and FIG. 13B is a schematic plan view illustrating the positionalrelationship between the first electrode and protrusions in thesemiconductor light-emitting device according to the second embodiment;

FIG. 14 is a schematic cross-sectional view of a semiconductorlight-emitting device according to a third embodiment;

FIG. 15 is a schematic cross-sectional view of a semiconductorlight-emitting device according to a fourth embodiment;

FIG. 16A is a schematic plan view illustrating the positionalrelationship between protrusions and a second electrode in asemiconductor light-emitting device according to a fifth embodiment, andFIG. 16B is a schematic cross-sectional view taken along the lineXVIb-XVIb in FIG. 16A;

FIG. 17A is a schematic plan view illustrating the positionalrelationship between a first electrode and second electrodes in asemiconductor light-emitting device according to a sixth embodiment, andFIG. 17B is a schematic plan view illustrating the positionalrelationship between protrusions and the second electrodes in thesemiconductor light-emitting device according to the sixth embodiment;

FIG. 18A is a schematic plan view illustrating the positionalrelationship between a first electrode and a second electrode in asemiconductor light-emitting device according to a seventh embodiment,and FIG. 18B is a schematic plan view illustrating the positionalrelationship between protrusions and the second electrode in thesemiconductor light-emitting device according to the seventh embodiment;

FIG. 19 is a schematic cross-sectional view of a semiconductorlight-emitting device according to an eighth embodiment;

FIG. 20 is a schematic cross-sectional view of a GaAs infraredlight-emitting device disclosed in Japanese Patent No. 3312049; and

FIG. 21 is a schematic cross-sectional view of a micro LED arraydisclosed in Japanese Patent No. 4830356.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will be described below. Likereference numerals denote like parts or equivalents thereof throughoutthe figures illustrating the embodiments.

First Embodiment

FIG. 1 is a schematic cross-sectional view of a semiconductorlight-emitting device according to a first embodiment. As illustrated inFIG. 1, the semiconductor light-emitting device according to the firstembodiment includes a first conductivity type semiconductor 4, forexample, an n-type semiconductor, a second conductivity typesemiconductor 6, for example, a p-type semiconductor, and an activelayer 5 disposed between a second main surface 4 b of the firstconductivity type semiconductor 4 and a first main surface 6 a of thesecond conductivity type semiconductor 6. In the first embodiment, thefirst conductivity type semiconductor 4 may be an n-type nitridesemiconductor clad layer containing n-type Al_(x1)Ga_(y1)N (0<x1≦1,0≦y1<1). The second conductivity type semiconductor 6 may be amultilayer body composed of a p-type nitride semiconductor layer 7containing p-type Al_(x2)Ga_(y2)N (0<x2≦1, 0≦y2<1) and a p-type nitridesemiconductor highly doped layer 8 containing p-type Al_(x3)Ga_(y3)N(0<x3≦1, 0≦y3<1). The active layer 5 may be a single quantum well (SQW)or multiple quantum well (MQW) active layer containing Al_(x4)Ga_(y4)N(0<x4≦1, 0≦y4<1).

A first main surface 4 a of the first conductivity type semiconductor 4faces a second main surface 6 b of the second conductivity typesemiconductor 6 with the first conductivity type semiconductor 4, theactive layer 5, and the second conductivity type semiconductor 6interposed therebetween. The first main surface 4 a of the firstconductivity type semiconductor 4 includes an electrode forming region(a first region 16) that includes a first electrode 13 serving as ann-electrode, and an electrode-free region (a second region 17) thatincludes no first electrode 13. The first main surface 4 a of the firstconductivity type semiconductor 4 is a light extraction surface of thesemiconductor light-emitting device according to the first embodiment.

Protrusions 9 are disposed in a region (a third region 61) of the secondmain surface 6 b of the second conductivity type semiconductor 6, whichfaces a region (the first region 16) that includes the first electrode13 on the first main surface 4 a of the first conductivity typesemiconductor 4. The p-type nitride semiconductor highly doped layer 8is disposed in a region (a fourth region 62) of the second main surface6 b of the second conductivity type semiconductor 6, which faces aregion (the second region 17) that includes no first electrode 13 on thefirst main surface 4 a of the first conductivity type semiconductor 4.The p-type nitride semiconductor highly doped layer 8 contains magnesium(Mg) as a p-type impurity.

The protrusions 9 contain a dielectric material and protrude from thesecond main surface 6 b of the second conductivity type semiconductor 6in a direction away from the active layer 5. The intervals 15 betweenthe protrusions 9 are the shortest distances between adjacent tops ofthe protrusions 9. The p-type nitride semiconductor highly doped layer 8protrudes from the p-type nitride semiconductor layer 7 in a directionaway from the active layer 5 and has a higher p-type impurityconcentration than the p-type nitride semiconductor layer 7.

A second electrode 18 serving as a p-electrode is disposed on a mainsurface of the p-type nitride semiconductor highly doped layer 8opposite the active layer 5. The p-type nitride semiconductor highlydoped layer 8, the protrusions 9, and the second electrode 18 arecovered with a metal layer 10. The metal layer 10 is mechanically andelectrically bonded to an electrically conductive substrate 12 with anelectrically conductive bonding layer 11.

FIG. 2 is a schematic enlarged cross-sectional view of a portion withinthe broken line 14 in FIG. 1. FIG. 3A is a schematic plan view of theprotrusions 9 viewed in the direction of the arrow 19 in FIG. 2, andFIG. 3B is a schematic plan view of one of the protrusions 9 illustratedin FIG. 3A. In the first embodiment, the protrusions 9 are quadrangularpyramids that protrude in a direction away from the active layer 5. Thetops of the quadrangular pyramidal protrusions 9 are the farthest pointsfrom the active layer 5. The intervals 15 between the protrusions 9 aregreater than the wavelength λ1 of light emitted from the active layer 5propagating through the medium of the protrusions 9.

In the semiconductor light-emitting device according to the firstembodiment, the protrusions 9 containing a dielectric material aredisposed in the region (the third region 61) of the second main surface6 b of the second conductivity type semiconductor 6 facing the firstelectrode 13, and the intervals 15 between the protrusions 9 are greaterthan the wavelength λ1 of light emitted from the active layer 5 in themedium of the protrusions 9. This can reduce the amount of lighttraveling to the first electrode 13 out of light emitted from the activelayer 5, propagating through the second conductivity type semiconductor6, reflected from the interface between the protrusions 9 and anothermedium (the metal layer 10 in the first embodiment), and traveling inthe direction of the first electrode 13. This can reduce the amount oflight absorbed by the first electrode 13 and improve light extractionefficiency (the ratio of the amount of light extracted from the deviceto the amount of electric current flowing into the device) in thesemiconductor light-emitting device according to the first embodiment.

The principle of controlling the direction of light reflection with theprotrusions 9 will be described below with reference to FIGS. 4A to 4C.In FIG. 4A, incident light 20 is reflected as reflected light 21 by aninterface 22 between the protrusions 9 and a medium (the metal layer 10in the first embodiment) adjacent to the protrusions 9. The wavelengthλ1 of the incident light 20 in the medium of the protrusions 9 isrepresented by λ1=λ0/n, wherein n denotes the refractive index of thedielectric material of the protrusions 9, and λ0 denotes the wavelengthof the incident light 20 in a vacuum.

FIGS. 4B and 4C are schematic enlarged cross-sectional views of theprotrusions 9. When incident light 20 propagating in the directionperpendicular to the second main surface 6 b of the second conductivitytype semiconductor 6 is incident on the protrusions 9, the incidentlight 20 is scattered at each point on the inclined surfaces of theprotrusions 9 according to the Huygens' principle.

FIG. 4B illustrates light scattering in the case where the intervals 15between the protrusions 9 are greater than the wavelength λ1 of lightemitted from the active layer 5 in the medium of the protrusions 9. Whenthe incident light 20 propagates from the active layer 5 to the secondconductivity type semiconductor 6, is reflected from an interface, andis incident at each point on the inclined surfaces of the protrusions 9,the incident light 20 is scattered as a spherical wave at each point andforms wavefronts of scattered light 25 in the same phase. FIG. 4Billustrates the envelope surface 26 of the wavefronts of scattered light25. The traveling direction of the scattered light 21 of the incidentlight 20 propagating in the direction perpendicular to the second mainsurface 6 b of the second conductivity type semiconductor 6 and incidenton the protrusions 9 is perpendicular to the envelope surface 26 and isnot perpendicular to the second main surface 6 b of the secondconductivity type semiconductor 6.

FIG. 4C illustrates light scattering in the case where the intervals 15between the protrusions 9 are smaller than or equal to the wavelength λ1of light emitted from the active layer 5 in the medium of theprotrusions 9. In this case, the envelope surface of wavefronts ofscattered light 25 of the incident light 20 propagating from the activelayer 5 to the second conductivity type semiconductor 6, reflected froman interface, and incident at each point on the inclined surfaces of theprotrusions 9 is substantially flat, although the envelope surface hasfine asperities. Thus, in this case, the traveling direction of thescattered light 21 of the incident light 20 propagating in the directionperpendicular to the second main surface 6 b of the second conductivitytype semiconductor 6 and incident on the protrusions 9 is perpendicularto the second main surface 6 b of the second conductivity typesemiconductor 6.

WO2011/065571A1 discloses that the traveling direction of the reflectedlight 21 can be controlled in the case where the intervals 15 betweenthe protrusions 9 are greater than the wavelength λ1 of light emittedfrom the active layer 5 in the medium of the protrusions 9.

Thus, in the semiconductor light-emitting device according to the firstembodiment, the interface between the protrusions 9 and another mediumcan change the traveling direction of light propagating in the directionperpendicular to the second main surface 6 b of the second conductivitytype semiconductor 6 and incident on and reflected from the protrusions9 such that the reflected light does not travel toward the firstelectrode 13. This can reduce the amount of light absorbed by the firstelectrode 13 and improve light extraction efficiency.

Theoretically, the textured structure of the p-type semiconductor layer126 illustrated in FIG. 21 and described in Japanese Patent No. 4830356can also control the traveling direction of light as in thesemiconductor light-emitting device according to the first embodiment.However, in order to form the textured structure on the p-typesemiconductor layer 126, the p-type semiconductor layer 126 has acertain thickness due to the device structure described in JapanesePatent No. 4830356. In the device structure described in Japanese PatentNo. 4830356, therefore, the p-type semiconductor layer 126 causes agreat loss due to absorption of light. By contrast, in the semiconductorlight-emitting device according to the first embodiment, the protrusions9 containing a dielectric material instead of the second conductivitytype semiconductor 6 have the function of controlling the travelingdirection of light. This can reduce the thickness of the secondconductivity type semiconductor 6. Thus, in the semiconductorlight-emitting device according to the first embodiment, the thicknessof the second conductivity type semiconductor 6 can be reduced tominimize loss due to absorption of light in the second conductivity typesemiconductor 6 and further improve light extraction efficiency.

In the semiconductor light-emitting device according to the firstembodiment, the second electrode 18 is disposed in the fourth region 62of the second main surface 6 b of the second conductivity typesemiconductor 6, which does not face the first electrode 13. Thus, thefirst electrode 13 and the second electrode 18 do not face each otheracross the active layer 5. This can widen the electric current path fromthe second electrode 18 to the first electrode 13 and extend thelight-emitting region in the active layer 5.

In the semiconductor light-emitting device according to the firstembodiment, the metal layer 10 covering the protrusions 9 and the secondelectrode 18 is electrically and mechanically bonded to the electricallyconductive substrate 12 with the electrically conductive bonding layer11. Thus, the semiconductor light-emitting device according to the firstembodiment can easily establish electrical continuity and simplify aprocess of mounting the device, thus resulting in lower manufacturingcosts.

In the semiconductor light-emitting device according to the firstembodiment, the protrusions 9 and the metal layer 10 covering theprotrusions 9 form an interface, and the amount of light passing throughthe interface can be reduced.

In the device structure illustrated in FIG. 20 and described in JapanesePatent No. 3312049, the V-shaped groove 117, which divides the PNjunction plane 113, reduces the area of the PN junction plane 113 thatis involved in light emission. By contrast, the semiconductorlight-emitting device according to the first embodiment has no groovethat divides the active layer 5 and can avoid such a problem.

A method for manufacturing the semiconductor light-emitting deviceaccording to the first embodiment will be described below with referenceto the schematic cross-sectional views of FIGS. 5 to 12.

First, as illustrated in FIG. 5, an AlN buffer layer 2, an AlGaNunderlayer 3, the first conductivity type semiconductor 4, the activelayer 5, the p-type nitride semiconductor layer 7, and the p-typenitride semiconductor highly doped layer 8 are stacked on a sapphiresubstrate 1 in this order by a metal organic chemical vapor deposition(MOCVD) method. The sapphire substrate 1 may be replaced by an AlNsubstrate.

As illustrated in FIG. 6, a portion of the p-type nitride semiconductorhighly doped layer 8 other than a portion in which the second electrode18 is to be formed is then removed. The p-type nitride semiconductorhighly doped layer 8 can be removed, for example, by dry etching, suchas reactive ion etching, after a resist pattern is formed on the p-typenitride semiconductor highly doped layer 8 by photolithography. Removalof an unnecessary portion of the p-type nitride semiconductor highlydoped layer 8 can reduce the amount of light emitted from the activelayer 5 and absorbed by the p-type nitride semiconductor highly dopedlayer 8 and thereby improve light extraction efficiency.

After the p-type nitride semiconductor highly doped layer 8 is partlyremoved, the semiconductor wafer is heated. For example, thesemiconductor wafer can be heated to 800° C. or more in a heat treatmentfurnace.

As illustrated in FIG. 7, the second electrode 18 is then formed on thep-type nitride semiconductor highly doped layer 8. For example, thesecond electrode 18 can be formed by forming a resist pattern on thep-type nitride semiconductor highly doped layer 8 by photolithography,successively forming a nickel (Ni) layer having a thickness of 20 nm anda gold (Au) layer having a thickness of 20 nm by an electron-beamevaporation method, and performing lift-off. Instead of the Ni and Aulayers, the second electrode 18 may be composed of platinum (Pt) and Aulayers or palladium (Pd) and Au layers. The second electrode 18 may beformed by a known sputtering method as well as the electron-beamevaporation method. The second electrode 18 can provide good ohmiccharacteristics and provide good adhesion to the electrically conductivesubstrate 12. Before the protrusions 9 are formed, the p-type nitridesemiconductor highly doped layer 8 can be covered with the secondelectrode 18 in order to reduce damage to the p-type nitridesemiconductor highly doped layer 8 in the subsequent process.

As illustrated in FIG. 8, the protrusions 9 are then formed on thep-type nitride semiconductor layer 7. For example, the protrusions 9 canbe formed as described below. First, a dielectric film, such as an AlNfilm, is formed on the p-type nitride semiconductor layer 7 by a knownsputtering method. A resist pattern is then formed on the dielectricfilm by photolithography. The dielectric film is then partly removed bydry etching, such as reactive ion etching, so as to form a periodic fineuneven pattern. The protrusions 9 can be formed in this manner. Lighthaving a wavelength in an ultraviolet region (1 to 400 nm) has arefractive index in the range of approximately 2.3 to 2.6 inAl_(x)Ga_(y)N (0<x≦1, 0≦y<1). AlN has a refractive index ofapproximately 2.3. When the protrusions 9 are formed of AlN, this canreduce the refractive index difference at the interface between theprotrusions 9 and the p-type nitride semiconductor layer 7 and reducetotal reflection, thus allowing the reflection direction of more lightto be controlled. The protrusions 9 may be formed of a material otherthan AlN, for example, a dielectric material that has a refractive indexclose to the refractive index of the p-type nitride semiconductor layer7 for light having a wavelength in an ultraviolet region (1 to 400 nm)and is transparent to the light. The protrusions 9 may be formed at adesired etching angle (taper angle) by changing the etching conditions,such as the ambient gas, of dry etching, such as reactive ion etching,so as to adjust the dry etching rate in the thickness direction and inthe in-plane direction. The protrusions 9 may be quadrangular pyramids.

The protrusions 9 are formed such that the intervals 15 between theprotrusions 9 are smaller than or equal to the wavelength λ1 of lightemitted from the active layer 5 in the medium of the protrusions 9. Theintervals 15 between the protrusions 9 can be determined by dividing thesemiconductor light-emitting device or by cross-sectioning thesemiconductor light-emitting device with a focused ion beam (FIB) and bymeasuring the distance between adjacent tops of the protrusions 9 withan electron microscope. The wavelength λ1 in the medium of theprotrusions 9 can be calculated by observing light emitted from thesemiconductor light-emitting device with a photodetector, determiningthe wavelength λ0 in air, and determining the refractive index n of theprotrusions 9 by spectroscopic ellipsometry analysis. The wavelength λ1is represented by λ1 =(λ0×n0)/n, wherein λ0 denotes the wavelength inair, n0 denotes the refractive index of air, and n denotes therefractive index of the protrusions 9.

As illustrated in FIG. 9, the protrusions 9, the p-type nitridesemiconductor highly doped layer 8, and the second electrode 18 are thencovered with the metal layer 10. The metal layer 10 may be formed bystacking an aluminum (Al) layer having a thickness of 300 nm and a Aulayer having a thickness of 300 nm in this order by a sputtering method.A reflection interface between the metal layer 10 containing Al andhaving high reflectance for light having a wavelength in an ultravioletregion and the protrusions 9 containing a dielectric material can reducethe amount of light passing through the reflection interface. The metallayer 10 can enhance bonding to the electrically conductive substrate 12with the electrically conductive bonding layer 11 as compared with theprotrusions 9 and can improve the yield.

As illustrated in FIG. 10, the metal layer 10 and the electricallyconductive substrate 12 are then bonded together with the electricallyconductive bonding layer 11. The metal layer 10 and the electricallyconductive substrate 12 can be bonded together with the electricallyconductive bonding layer 11 as described below. First, a bonding metallayer (not shown), such as a multilayer body composed of a Ni layerhaving a thickness of 20 nm and a Au layer having a thickness of 150 nm,is formed on the electrically conductive substrate 12, such as a CuWsubstrate or a Si substrate doped with a p-type semiconductor. Theelectrically conductive bonding layer 11 is then placed so as to facethe metal layer 10.

The electrically conductive bonding layer 11 may be a thermosettingelectrically conductive adhesive containing silver (Ag) or may be formedof Au, tin (Sn), Pd, indium (In), titanium (Ti), Ni, tungsten (W),molybdenum (Mo), Au—Sn, Sn—Pd, In—Pd, Ti—Pt—Au, or Ti—Pt—Sn. Theelectrically conductive bonding layer 11 formed of such a material canbe bonded to the metal layer 10 through an eutectic reaction. Aneutectic layer formed by the eutectic reaction and the metal layer 10diffuse into each other and form eutectic crystals.

The sapphire substrate 1 and the electrically conductive substrate 12are then heat-pressed. When the electrically conductive bonding layer 11is a thermosetting electrically conductive adhesive, the sapphiresubstrate 1 and the electrically conductive substrate 12 may be pressedat hundreds of newtons to several kilonewtons, may be heated toapproximately 150° C. to 400° C., and may be held in a vacuum, in anitrogen atmosphere, or in the air for approximately 15 minutes. Whilethe sapphire substrate 1 and the electrically conductive substrate 12are heat-pressed, the electrically conductive bonding layer 11 melts andthen solidifies, thereby bonding the metal layer 10 and the electricallyconductive substrate 12 together.

The bonding conditions without pressing may include heating atapproximately 200° C. in a vacuum, in a nitrogen atmosphere, or in theair for approximately 60 minutes. The bonding conditions depend on thecharacteristics of the material of the electrically conductive bondinglayer 11. The electrically conductive substrate 12, the metal layer 10,and the second electrode 18 are electrically bonded together with theelectrically conductive bonding layer 11, thereby enabling electriccurrent input.

Before the next laser lift-off (LLO) process, the back side (a surfaceopposite the electrically conductive bonding layer 11) of the sapphiresubstrate 1 may be ground and polished such that the sapphire substrate1 has a desired thickness.

As illustrated in FIG. 11, the sapphire substrate 1 is then separatedfrom the AlN buffer layer 2. For example, the sapphire substrate 1 isseparated from the AlN buffer layer 2 by a LLO method. Morespecifically, the sapphire substrate 1 is separated from the AlN bufferlayer 2 by irradiating the back side of the sapphire substrate 1 with anexcimer laser beam having a wavelength of approximately 193 nm. Theexcimer laser beam may have an energy density in the range ofapproximately 500 to 8000 mJ/cm².

As illustrated in FIG. 12, the AlN buffer layer 2 and the AlGaNunderlayer 3 are then separated from the first conductivity typesemiconductor 4. For example, the AlN buffer layer 2 and the AlGaNunderlayer 3 can be separated from the first conductivity typesemiconductor 4 by immersing the semiconductor wafer in hydrofluoricacid at 40° C. or more after the sapphire substrate 1 is separated. Morespecifically, after the sapphire substrate 1 is separated, thesemiconductor wafer can be immersed in hydrofluoric acid at 60° C. for15 minutes. In such hydrofluoric acid treatment, a residual Al inclusionof the first conductivity type semiconductor 4 characteristic of the LLOmethod can be removed by hydrofluoric acid. The Al inclusion canfunction as an etching mask and suppress the formation of pillarprojections on the first conductivity type semiconductor 4, thusflattening the surface of the first conductivity type semiconductor 4.This can improve the yield in a process of forming the first electrode13 and a process of dividing a device described later.

The surface of the first conductivity type semiconductor 4 is thenpartly removed by dry etching. Thus, the first main surface 4 a of thefirst conductivity type semiconductor 4 is exposed. The first mainsurface 4 a of the first conductivity type semiconductor 4 is exposed bydry etching, such as reactive ion etching with chlorine (Cl) gas.

A resist pattern is then formed on the first main surface 4 a of thefirst conductivity type semiconductor 4 by photolithography. A metalfilm for forming the first electrode 13 is then formed on the resistpattern. The first electrode 13 is then formed by lift-off, asillustrated in FIG. 1. For example, the first electrode 13 can be formedby forming a Ti layer having a thickness of 25 nm and an Al layer havinga thickness of 200 nm on the resist pattern in this order by anelectron-beam evaporation method and then performing lift-off. The firstelectrode 13 may be formed by a known sputtering method instead of theelectron-beam evaporation method.

The semiconductor wafer can be divided into semiconductor light-emittingdevices illustrated in FIG. 1 by a known method, such as diamondscribing, laser scribing, blade dicing, blade breaking, or rollerbreaking.

Second Embodiment

FIG. 13A is a schematic plan view illustrating the positionalrelationship between a first electrode 13 and a second electrode 18 in asemiconductor light-emitting device according to a second embodiment.FIG. 13B is a schematic plan view illustrating the positionalrelationship between protrusions 9 and the second electrode 18 in thesemiconductor light-emitting device according to the second embodiment.As illustrated in FIGS. 13A and 13B, in the semiconductor light-emittingdevice according to the second embodiment, the second electrode 18 issurrounded by the first electrode 13, and the protrusions 9 face thefirst electrode 13. Such a structure allows the electric current flowninto an active layer 5 to diffuse in a wider region and can reduce thearea of the first electrode 13, thereby improving light extractionefficiency.

The second electrode 18 includes first line electrodes 18 b extending ina first direction and a second line electrode 18 a extending in a seconddirection, which is different from the first direction. The first lineelectrodes 18 b cross the second line electrode 18 a and areelectrically connected to each other with the second line electrode 18a.

Third Embodiment

FIG. 14 is a schematic cross-sectional view of a semiconductorlight-emitting device according to a third embodiment. As illustrated inFIG. 14, the semiconductor light-emitting device according to the thirdembodiment is characterized in that there is no p-type nitridesemiconductor highly doped layer 8, a second conductivity typesemiconductor is composed of a p-type nitride semiconductor layer 7alone, the p-type nitride semiconductor layer 7 has a thickness t₂smaller than the thickness t₁ of a first conductivity type semiconductor4 and the wavelength λ1 of light emitted from an active layer 5 in themedium of protrusions 9, and the protrusions 9 have a thickness t₃larger than the thickness t₂ of the p-type nitride semiconductor layer7. The thickness t₁ of the first conductivity type semiconductor 4 isthe shortest distance between a first main surface 4 a and a second mainsurface 4 b of the first conductivity type semiconductor 4. Thethickness t₂ of the p-type nitride semiconductor layer 7 is the shortestdistance between a first main surface 6 a and a second main surface 6 bof the p-type nitride semiconductor layer 7, which constitutes thesecond conductivity type semiconductor. The thickness t₃ of theprotrusions 9 is the shortest distance between the tops and bottoms ofthe protrusions 9.

An increased thickness t₁ of the first conductivity type semiconductor 4results in a decreased number of crystal defects and wider diffusion ofthe electric current from the first electrode 13. Thus, the firstconductivity type semiconductor 4 has a thickness t₁ of 300 nm or more,for example.

However, thick p-type nitride semiconductor films have a great opticalabsorption loss and make it difficult to extract light. Thus, when thep-type nitride semiconductor layer 7 is a nitride semiconductor, such asp-type GaN or p-type Al_(x2)Ga_(y2)N (0<x2≦1, 0≦y2<1) having a low Alcontent, the p-type nitride semiconductor layer 7 has a small thicknesst₂ of 200 nm or less, for example. The p-type nitride semiconductorlayer 7 having a thickness t₂ smaller than the thickness t₁ of the firstconductivity type semiconductor 4 allows the electric current to flowefficiently into the active layer 5 and allows light generated in theactive layer 5 to be efficiently extracted.

The intervals 15 between the protrusions 9 are greater than thewavelength of light emitted from the active layer 5 in the medium of theprotrusions 9, as in the first and second embodiments, in order tocontrol the direction of light reflection. When the emission wavelengthof light emitted from the active layer 5 ranges from 220 to 350 nm, theintervals 15 between the protrusions 9 can be 660 nm or more, in orderto improve light extraction efficiency.

When the thickness t₃ of the protrusions 9 is greater than the thicknesst₂ of the p-type nitride semiconductor layer 7, the inclinations of theinclined surfaces of the protrusions 9 can be easily controlled. Thus,reflected light at the interface between the protrusions 9 and the metallayer 10 can be easily directed to a region that includes no firstelectrode 13, and the light extraction efficiency can be easilyimproved.

The semiconductor light-emitting device according to the thirdembodiment is also characterized in that the total area of a secondregion 17, which includes no first electrode 13 on the first mainsurface 4 a of the first conductivity type semiconductor 4, is largerthan the total area of a first region 16, which includes a firstelectrode 13. This can increase the amount of light extracted from thefirst main surface 4 a of the first conductivity type semiconductor 4and tends to further improve light extraction efficiency. In order toimprove light extraction efficiency, the total area of the second region17 can be at least three times the total area of the first region 16.

The other description of the third embodiment is basically the same asthe description of the first and second embodiments and is omitted.

Fourth Embodiment

FIG. 15 is a schematic cross-sectional view of a semiconductorlight-emitting device according to a fourth embodiment. Thesemiconductor light-emitting device according to the fourth embodimentis characterized in that there is no metal layer 10, and protrusions 9and an electrically conductive bonding layer 11 form a reflectioninterface. Such a structure can also reduce the amount of light passingthrough the reflection interface between the protrusions 9 and theelectrically conductive bonding layer 11. Furthermore, a process ofmanufacturing the semiconductor light-emitting device according to thefourth embodiment can be simplified without a process of forming a metallayer 10, thus resulting in lower manufacturing costs.

The other description of the fourth embodiment is basically the same asthe description of the first to third embodiments and is omitted.

Fifth Embodiment

FIG. 16A is a schematic plan view illustrating the positionalrelationship between protrusions 9 and a second electrode 18 in asemiconductor light-emitting device according to a fifth embodiment.FIG. 16B is a schematic cross-sectional view taken along the lineXVIb-XVIb in FIG. 16A. The semiconductor light-emitting device accordingto the fifth embodiment is characterized in that the protrusions 9 havethe shape of stripes of triangular prisms extending along the peripheryof the device.

The other description of the fifth embodiment is basically the same asthe description of the first to fourth embodiments and is omitted.

Sixth Embodiment

FIG. 17A is a schematic plan view illustrating the positionalrelationship between a first electrode 13 and second electrodes 18 in asemiconductor light-emitting device according to a sixth embodiment.FIG. 17B is a schematic plan view illustrating the positionalrelationship between protrusions 9 and the second electrodes 18 in thesemiconductor light-emitting device according to the sixth embodiment.The semiconductor light-emitting device according to the sixthembodiment is characterized in that the second electrodes 18 areseparated from each other. The first electrode 13 has a grid-likepattern, and the second electrodes 18 are rectangular. Each of therectangular second electrodes 18 faces a corresponding rectangularregion within the first electrode 13. Such a structure also allows theelectric current to flow into a wider region of an active layer 5 andcan reduce the area of the first electrode 13, thereby improving lightextraction efficiency.

The other description of the sixth embodiment is basically the same asthe description of the first to fifth embodiments and is omitted.

Seventh Embodiment

FIG. 18A is a schematic plan view illustrating the positionalrelationship between a first electrode 13 and a second electrode 18 in asemiconductor light-emitting device according to a seventh embodiment.FIG. 18B is a schematic plan view illustrating the positionalrelationship between protrusions 9 and the second electrode 18 in thesemiconductor light-emitting device according to the seventh embodiment.The semiconductor light-emitting device according to the seventhembodiment is characterized in that the first electrode 13 and thesecond electrode 18 are comb-like and interdigitated. Such a structurealso allows the electric current to flow into the entire active layer 5and can reduce the area of the first electrode 13, thereby improvinglight extraction efficiency.

The other description of the seventh embodiment is basically the same asthe description of the first to sixth embodiments and is omitted.

Eighth Embodiment

FIG. 19 is a schematic cross-sectional view of a semiconductorlight-emitting device according to an eighth embodiment. Thesemiconductor light-emitting device according to the eighth embodimentis characterized in that protrusions 9 have a triangular cross sectionand, in a triangular cross section of one of the protrusions 9 closestto the periphery of the semiconductor light-emitting device, a side 9 aof the closest protrusion 9 adjacent to the periphery of thesemiconductor light-emitting device is longer than a side 9 b of theclosest protrusion 9 away from the periphery of the semiconductorlight-emitting device. In such a structure, the protrusion 9 closest tothe periphery of the semiconductor light-emitting device can returnlight emitted outward from the semiconductor light-emitting device tothe inside of the semiconductor light-emitting device and therebyimprove light extraction efficiency. In order to further improve lightextraction efficiency, one of the protrusions 9 closest to the peripheryof the semiconductor light-emitting device can have a right-angledtriangular cross section in which a side 9 a of the closest protrusion 9adjacent to the periphery of the semiconductor light-emitting device islonger than an inner side 9 b.

The other description of the eighth embodiment is basically the same asthe description of the first to seventh embodiments and is omitted.

Supplementary Notes

(1) An embodiment disclosed herein is a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) that includes a firstconductivity type semiconductor, a second conductivity typesemiconductor, an active layer between the first conductivity typesemiconductor and the second conductivity type semiconductor, a firstelectrode disposed on a first main surface of the first conductivitytype semiconductor, a second electrode disposed on a second main surfaceof the second conductivity type semiconductor, and a plurality ofprotrusions disposed on the second main surface of the secondconductivity type semiconductor. The first main surface of the firstconductivity type semiconductor faces the second main surface of thesecond conductivity type semiconductor with the first conductivity typesemiconductor, the active layer, and the second conductivity typesemiconductor interposed therebetween. The protrusions are disposed inat least part of a region of the second main surface of the secondconductivity type semiconductor facing each of the first electrodes. Thesecond electrode is disposed in at least part of a region of the secondmain surface of the second conductivity type semiconductor other thanthe region in which the protrusions are disposed. The protrusionsprotrude from the second main surface of the second conductivity typesemiconductor in a direction away from the active layer. The protrusionscontain a dielectric material. The protrusions are separated by aninterval longer than the wavelength of light emitted from the activelayer in the medium of the protrusions. Such a structure can provide asemiconductor light-emitting device containing Al_(x)Ga_(y)N (0<x≦1,0≦y<1) having improved light extraction efficiency.

(2) A semiconductor light-emitting device according to an embodimentdisclosed herein may further include a metal layer covering protrusions.Such a structure can also provide a semiconductor light-emitting devicecontaining Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(3) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a metal layer may be disposed on a second electrode.Such a structure can also provide a semiconductor light-emitting devicecontaining Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(4) A semiconductor light-emitting device according to an embodimentdisclosed herein may further include an electrically conductivesubstrate and an electrically conductive bonding layer for bonding theelectrically conductive substrate and a metal layer together. Such astructure can also provide a semiconductor light-emitting devicecontaining Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(5) A semiconductor light-emitting device according to an embodimentdisclosed herein may further include an electrically conductivesubstrate and an electrically conductive bonding layer for bonding theelectrically conductive substrate and protrusions. Such a structure canalso provide a semiconductor light-emitting device containingAl_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(6) In a semiconductor light-emitting device according to an embodimentdisclosed herein, an electrically conductive bonding layer may bedisposed on and electrically connected to a second electrode. Such astructure can also provide a semiconductor light-emitting devicecontaining Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(7) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a second conductivity type semiconductor may include aprojection in at least part of a second region of the secondconductivity type semiconductor in a direction away from an activelayer. Such a structure can also provide a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved lightextraction efficiency.

(8) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a second electrode may be disposed on a projection ofa second conductivity type semiconductor. Such a structure can alsoprovide a semiconductor light-emitting device containing Al_(x)Ga_(y)N(0<x≦1, 0≦y<1) having improved light extraction efficiency.

(9) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a projection of a second conductivity typesemiconductor may contain magnesium. Such a structure can also provide asemiconductor light-emitting device containing Al_(x)Ga_(y)N (0<x≦1,0≦y<1) having improved light extraction efficiency.

(10) In a semiconductor light-emitting device according to an embodimentdisclosed herein, protrusions may be disposed in a region other than aprojection of a second conductivity type semiconductor. Such a structurecan also provide a semiconductor light-emitting device containingAl_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(11) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a second electrode may include first line electrodesextending in a first direction and a second line electrode extending ina second direction, which is different from the first direction, and thefirst line electrodes may cross the second line electrode. Such astructure can also provide a semiconductor light-emitting devicecontaining Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(12) In a semiconductor light-emitting device according to an embodimentdisclosed herein, there may be second electrodes separated from eachother. Such a structure can also provide a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved lightextraction efficiency.

(13) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a first electrode and a second electrode may becomb-like and interdigitated. Such a structure can also provide asemiconductor light-emitting device containing Al_(x)Ga_(y)N (0<x≦1,0≦y<1) having improved light extraction efficiency.

(14) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a second conductivity type semiconductor may have athickness smaller than the thickness of a first conductivity typesemiconductor and the wavelength of light emitted from an active layerin the medium of protrusions, and the protrusions may have a greaterthickness than the second conductivity type semiconductor. Such astructure can also provide a semiconductor light-emitting devicecontaining Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(15) In a semiconductor light-emitting device according to an embodimentdisclosed herein, the thickness of a first conductivity typesemiconductor may be the shortest distance between a first main surfaceand a second main surface of the first conductivity type semiconductor.The second main surface faces the first main surface and an activelayer. Such a structure can also provide a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved lightextraction efficiency.

(16) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a region of a first main surface of a firstconductivity type semiconductor in which a first electrode is notdisposed may have a larger total area than a region in which the firstelectrode is disposed. Such a structure can also provide a semiconductorlight-emitting device containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) havingimproved light extraction efficiency.

(17) In a semiconductor light-emitting device according to an embodimentdisclosed herein, protrusions may be quadrangular pyramids. Such astructure can also provide a semiconductor light-emitting devicecontaining Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved light extractionefficiency.

(18) In a semiconductor light-emitting device according to an embodimentdisclosed herein, protrusions may have the shape of stripes oftriangular prisms extending along the periphery of the semiconductorlight-emitting device. Such a structure can also provide a semiconductorlight-emitting device containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) havingimproved light extraction efficiency.

(19) In a semiconductor light-emitting device according to an embodimentdisclosed herein, protrusions may have a triangular cross section and,in a triangular cross section of one of the protrusions closest to theperiphery of the semiconductor light-emitting device, a side of theclosest protrusion adjacent to the periphery of the semiconductorlight-emitting device may be longer than a side of the closestprotrusion away from the periphery of the semiconductor light-emittingdevice. Such a structure can also provide a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved lightextraction efficiency.

(20) In a semiconductor light-emitting device according to an embodimentdisclosed herein, a protrusion closest to the periphery of thesemiconductor light-emitting device may have a right-angled triangularcross section in which a side of the protrusion adjacent to theperiphery of the semiconductor light-emitting device is longer than aninner side of the protrusion. Such a structure can also provide asemiconductor light-emitting device containing Al_(x)Ga_(y)N (0<x≦1,0≦y<1) having improved light extraction efficiency.

(21) In a semiconductor light-emitting device according to an embodimentdisclosed herein, an active layer may contain Al_(x)Ga_(y)N (0<x≦1,0≦y<1). Such a structure can also provide a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved lightextraction efficiency.

(22) A semiconductor light-emitting device according to an embodimentdisclosed herein may have an emission wavelength in the range of 220 to350 nm. Such a structure can also provide a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved lightextraction efficiency.

(23) In a semiconductor light-emitting device according to an embodimentdisclosed herein, the intervals between protrusions may be 660 nm ormore. Such a structure can also provide a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1) having improved lightextraction efficiency.

These embodiments are originally envisaged to be combined as required.

It is to be understood that the embodiments disclosed herein areillustrated by way of example and not by way of limitation in allrespects. The scope of the present disclosure is defined by the appendedclaims rather than by the description preceding them. All modificationsthat fall within the scope of the claims and the equivalents thereof aretherefore intended to be embraced by the claims.

An embodiment disclosed herein relates to a semiconductor light-emittingdevice containing Al_(x)Ga_(y)N (0<x≦1, 0≦y<1)and a method formanufacturing the semiconductor light-emitting device and moreparticularly to a method for manufacturing a semiconductorlight-emitting device including a process of removing a semiconductorgrowth substrate from a semiconductor wafer by a laser lift-off (LLO)method and a semiconductor light-emitting device manufactured by themethod.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2015-245130 filed in theJapan Patent Office on Dec. 16, 2015, the entire contents of which arehereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A semiconductor light-emitting device containingAl_(x)Ga_(y)N (0<x≦1, 0≦y<1), comprising: a first conductivity typesemiconductor; a second conductivity type semiconductor; an active layerbetween the first conductivity type semiconductor and the secondconductivity type semiconductor; a first electrode disposed on a firstmain surface of the first conductivity type semiconductor; a secondelectrode disposed on a second main surface of the second conductivitytype semiconductor; and a plurality of protrusions disposed on thesecond main surface of the second conductivity type semiconductor,wherein the first main surface of the first conductivity typesemiconductor faces the second main surface of the second conductivitytype semiconductor with the first conductivity type semiconductor, theactive layer, and the second conductivity type semiconductor interposedtherebetween, the protrusions are disposed in at least part of a regionof the second main surface of the second conductivity type semiconductorfacing the first electrode, the second electrode is disposed in at leastpart of a region of the second main surface of the second conductivitytype semiconductor other than the region in which the protrusions aredisposed, the protrusions protrude from the second main surface of thesecond conductivity type semiconductor in a direction away from theactive layer, the protrusions contain a dielectric material, and theprotrusions are separated by an interval longer than a wavelength oflight emitted from the active layer in a medium of the protrusions. 2.The semiconductor light-emitting device according to claim 1, furthercomprising a metal layer covering the protrusions.
 3. The semiconductorlight-emitting device according to claim 1, further comprising: anelectrically conductive substrate; and an electrically conductivebonding layer for bonding the electrically conductive substrate and themetal layer together.
 4. The semiconductor light-emitting deviceaccording to claim 1, wherein the second conductivity type semiconductorhas a thickness smaller than a thickness of the first conductivity typesemiconductor and the wavelength of light emitted from the active layerin the medium of the protrusions, and the protrusions have a greaterthickness than the second conductivity type semiconductor.
 5. Thesemiconductor light-emitting device according to claim 1, wherein aregion of the first main surface of the first conductivity typesemiconductor in which the first electrode is not disposed has a largertotal area than a region in which the first electrode is disposed.